This invention relates to a brushless drive system for brushless D.C. Motors. In particular, the invention relates to a brushless drive system having a switch array for driving a brushless D.C. motor where the switch array includes at least one pair of bi-directional switches and the rotational direction of the brushless D.C. motor can be changed by reversing the voltage polarity at the two terminals where the power source is applied to the switch array.
The advantageous attributes of brushless DC motors over conventional brush-type DC motors are well known. Some of them are: (1) longer lifetime and increased reliability due to the lack of brushes, (2) better thermal characteristics since the wound element is stationary and may be easily connected to a heatsink, (3) better motor characteristics in a given package size since the maximum motor current and speed are not limited by brush contact surface, (4) in general, lower rotor inertia for a given output resulting in better servo performance.
However, industry has never vigorously pursued programs to replace brush-type DC motors with brushless DC motors on a one-for-one basis.
Part of the hesitancy in adopting brushless motors unilaterally in place of brush-type motors has been due to: (1) the existence of operational systems that already incorporate brush-type motors (historical inertia), (2) a lack of understanding of the application of brushless motors to the user's advantage, and (3) the requirement of larger and more complicated electronic controls for brushless DC motors. This invention addresses (1) and (3) in that it presents the user with a device containing simple drive electronics that may be interfaced with the user's present servo amplifier and system.
The invention is based upon the present availability of power MOSFET semiconductors in wide voltage and current ranges. The MOSFET configuration used is known; documentation exists that refers to the configuration as "switch" and "high-current analog switch". See, for instance, the Siliconix Mospower Design Catalog, January 1983, pp. 6-43 to 6-5 and the Silconix Mospower Applications book, 1984, Chapter 6.13.9. MOSFET's have also been applied in the conventional "6-switch" configuration in the industry. However, none of the previous references refer to using this particular MOSFET configuration with brushless DC motors.